Packaging film laminates for food packaging applications, particularly for, high speed packaging applications, such as, for example, vertical form-fill-seal (VFFS) and/or horizontal form-fill-seal (HFFS) processes, are well known to those skilled in the art. Many of known film laminates for these applications have a generalized structure of A/B/C/B/D where A is an external heat-seal layer, B is an internal layer of nylon, C is an internal core layer of ethylene/vinyl alcohol copolymer, and D is an external abuse layer. For example, U.S. Pat. No. 4,909,726 to Bekele discloses a hot blown coextruded film for packaging meat which includes a core layer containing ethylene/vinyl alcohol copolymer surrounded by two adjacent layers comprising nylon. Suitable materials for use in the heat-seal layer include resins having a fractional melt index (less than 1.0 g/10 min) which are selected from the group consisting of ethylene alpha-olefin copolymers, low density polyethylenes, and ethylene ester copolymers. U.S. Pat. No. 6,562,476 to Shepard et al. describe coextruded blown film laminates for packaging food products, such as meat and cheese. Shepard et al. teach of films which include two internal layers of amorphous nylon having nylon nucleating agents, a core layer of ethylene/vinyl alcohol copolymer, and a sealant layer comprising a material selected from the group consisting of linear polyethylenes, ethylene alpha-olefin copolymers, ionomers, EMA, EMAA, or ethylene/vinyl acetate. Shepard et al. do not disclose the melt index of the sealable material. U.S. Pat. No. 6,682,825 to Kennedy et al. also describe film laminates for food packaging applications which include a core layer of ethylene/vinyl alcohol copolymer sandwiched between two layers of amorphous nylon. This patent teaches that the outer heat-seal layer has a thickness of about 7 to 10 percent based on the total thickness of the film. Kennedy et al. do not describe the melt index of the resins used for the heat-seal layer. U.S. Pat. No. 4,746,562 to Fant discloses film laminates particularly useful for form-fill-seal applications. Fant teaches using low density polyethylenes as suitable material for the sealant layer, but does not disclose the melt index of these resins.
It will be appreciated by those skilled in the art that film laminates having substantial amounts of high melt index material in one or more film layers, for example, a sealant layer, have inherently low melt strengths and are typically produced using a flat die process, such as, for example, cast extrusion. Those skilled in the art will also appreciate that thickness build-ups or gauge bands often form during the cast extrusion process and affect the package manufacturing process by requiring more operator intervention to the packaging equipment in order to convert these films into acceptable products. Generally, films having thickness variations will decrease production rates and increase production costs for both film and package manufacturers. It is also well known by those skilled in the art, that gauge bands may be minimized by randomizing the thickness variation during the extrusion process. One method of accomplishing randomization is by using blown film coextrusion techniques, such as, for example, single-bubble blown film coextrusion, double-bubble blown film coextrusion and the like. Applicants have discovered that films having significant amounts of high melt index material may be obtained using a blown film coextrusion process which provides packaging films having excellent sealing characteristics as required for form-fill-seal packaging applications, without sacrificing film quality and production efficacy.